Periodic trends are specific patterns in aspects of certain elements present in the periodic table.

Trends

Ionization Energy

Comparison of ionization energies of atoms in the periodic table reveals two trends:

1. Ionization energy generally increases from left to right within a given period (row)
2. Ionization energy generally decreases from top to bottom in a given group (column)

The first trend is generally because of the higher the number of protons in the atomic nucleus as you move to the right of the periodic table, because of the increased attractive forces between the nucleus and the outermost electrons, it becomes increasingly difficult to displace them from the atom.

The second trend is generally because of the addition of more electron shells as you go down the periodic table.

Effective Nuclear Charge

Effective nuclear charge follows two general trends in the periodic table.

1. Effective nuclear charge generally increases from left to right within a given period (row)
2. Effective nuclear charge generally decreases from top to bottom in a given group (column)

The first trend is generally because of the higher the number of protons in the atomic nucleus as you move to the right of the periodic table, because of the increase this means that the effect of increased shielding between new electrons is far less than the increase in the charge of the nucleus.

The second trend is due to additional electron shells being added to the element as you go down a group which has a greater effect than the addition of more protons.

Electron Affinity

Electron affinity follows two general trends in the periodic table.

1. Electron affinity generally increases from left to right within a given period (row), besides the noble gases.
2. Electron affinity generally decreases from top to bottom in a given group (column)

TODO: Explain why

Electronegativity

Electronegativity follows two general trends in the periodic table.

1. Electronegativity generally increases from left to right within a given period (row), besides helium, neon and argon which all have no electronegativity
2. Electronegativity generally decreases from top to bottom in a given group (column)

TODO: Explain why

Atomic Radius

Atomic radius follows two general trends in the periodic table.

1. Atomic radius generally increases from left to right within a given period (row).
2. Atomic radius generally decreases from top to bottom in a given group (column)

The first trend is generally because of the increase in effective nuclear charge as you move to the right of the periodic table while remaining in the same shell causing the electrons to be more tightly bound.

The second trend is due to additional electron shells being added to the element as you go down a group which causes the outermost electrons to become much farther away than in the previous shell.